This invention relates to the field of display systems, particularly to full color display systems using a single light modulator, more particularly to sequential full color display systems using falling raster or scrolling color methods.
Viewers evaluate display systems based on many criteria such as image size, resolution, contrast ratio, color purity, and brightness. Image brightness is a particularly important metric in many display markets since the available brightness can limit the image size of a projected image and controls how well the image can be seen in venues having high levels of ambient light.
Projection display designers increase the brightness of a given projection display by increasing the light source used to form the image. Increasing the light source, however, also increases the cost, size, and weight of the display system. Additionally, larger light sources generate additional heat that must be dissipated by the display.
Many other factors affect the brightness of the images produced by the display system. One of the major factors is the number of modulators used to modulate the light used to produce the image. Display systems that use a modulator with a very fast response time, such as the digital micromirror device (DMD(trademark)), can use a single modulator to create a full color image. Other display systems use three modulators, such as liquid crystal display (LCD) panels or DMDs, to create a full color image.
Micromirror-based display systems typically operate the micromirrors in a digital, or bistable, manner. Digital operation fully deflects a given micromirror to either a first position or a second position. The illumination optics of the display device illuminate the entire array of micromirror cells. Micromirrors deflected to the first position reflect light along a first path, whereas micromirrors deflected to a second position reflect light along a second path. The projection optics of the display system collects the light from the mirrors in the first position and focus the light onto an image plane. The light reflected by mirrors in the second position is prevented from reaching the image plane. An image pixel associated with a mirror in the first position is brightly illuminated, whereas an image pixel associated with mirrors in the second position are not illuminated.
Pulse width modulation creates the perception of gray scale intensities with a digital micromirror device or other spatial light modulator. When using pulse width modulation, a given micromirror element is rapidly turned on and off in response to a digital intensity word. The duty cycle of the mirror determines the total amount of light contributed to an image pixel. If the pixel is pulsed quickly enough, the human eye will accurately measure the average intensity of the pixel, but will fail to detect the pulsing.
Full-color images also are produced by taking advantage of the relatively slow response time of the human eye. Each frame period is divided into at least three periods. During each period, a primary color image is produced. If the primary color images are produced in rapid succession, the eye will perceive a single full-color-image.
An alternative to the sequential color display system is a three-modulator display system. The three-modulator display system is very similar to the sequential color display system in that they both form full color images by the combining three primary color images. The disadvantage of the three-modulator display system is the cost of the three modulators and the complex optics required both to split the white light beam from the light source into three primary color light beams and to recombine the modulated primary color light beams.
The disadvantage of the single-modulator sequential color display systems is its low image brightness. Because the white light source is time-divided into three primary color light beams, most of the light at any given time is not used. For example, when the blue primary color image is being formed, the green and red output of the white light source are filtered out of the light beam. Thus, a sequential color display system, while generally less expensive than the three-modulator display system, makes very inefficient use of the light produced by the light source.
The lost light not only reduces the brightness of the image produced by the display system, discarding the light creates several problems for the display system. The light filtered out of the light beam generally becomes stray light that the display system must control to prevent from reaching the image plane and degrading the contrast of the displayed image. The off-primary light is generally converted to heat. The heat must be dissipated by using larger fans, which in turn increase the noise produced by the display system and increase the size of the display system.
What is needed is an efficient illumination system that is capable of providing the efficiency of a three-modulator display system while taking advantage of the simplified optics and low cost of a one-modulator display system.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention that provides a method and system for sequential color recapture. One embodiment of the claimed invention provides a display system comprising: a light source for producing a beam of white light, an integrator for homogenizing the beam of white light, a filter for filtering the homogenized beam of white light and separating the homogenized beam of white light into a primary color beam of light traveling along a first path, and a remainder beam of light traveling along a second path, a spatial light modulator on the first path for selectively modulating the light traveling along the first path to form an image, and wherein a portion of the remainder beam of light is incident a second region of the filter and travels along the first path.
A second embodiment of the disclosed invention provides a display system comprising: a light source for producing a beam of white light, an integrator for homogenizing the beam of white light, a filter for filtering the homogenized beam of white light, the filter separating the homogenized beam of white light into a primary color beam of light traveling along a first path, and a remainder beam of light traveling along a second path, a spatial light modulator on the first path for receiving light traveling along the first path and selectively modulating the light traveling along the first path to form an image, and wherein the remainder beam re-enters the integrator and is re-transmitted by the integrator to the filter such that a portion of the remainder beam of light is incident a second region of the filter and travels along the first path.
A third embodiment of the disclosed invention provides a method of producing an image. The method comprises the steps of: providing a beam of white light, impinging the beam of white light on a first region of a dynamic filter, the first region of the dynamic filter transmitting a first primary portion and rejecting a remainder of the beam of light, modulating the first primary portion, impinging a portion of the remainder of the beam of light on a second region of the dynamic filter, the second region of the dynamic filter transmitting a second primary portion of the remainder of the beam of light, modulating the second primary portion of the beam of light, and focusing the modulated first and second primary portions of the beam of light on an image plane.
The disclosed invention provides the technical advantage of much higher illumination efficiency. Since all color components of the beam of light are used at all times, the disclosed system and method achieve three modulator panel system efficiencies using only a single modulator panel. The higher efficiency enables the use of lower cost light sources that have longer operational lives and produce less heat. The apparatus required to implement the disclosed invention is much less costly than the optics and modulator panels required to implement a three panel display solution. Because less heat is generated, the overall display system volume will decrease since there is a reduced need for cooling fans and air ducts.